Empirical and theoretical fusion barriers for1H and4He: Connections to evaporation from hot nuclei

Abstract

Fusion excitation functions for ~H and 4He have been compared to a one-dimensional, barrier-penetration model. In contrast to fusion for heavier nuclei this simple model is completely adequate, except for the statically deformed targed 233U. Empirical barrier heights are obtained and compared to those from two theoretical nuclear potentials. These empirical barriers (from cold reactants) are used as input for calculating evaporation spectra that arise from hot nuclear emitters. The excess of observed low-energy 1H and 4He emission signals information content concerning distortions of the hot nuclei.

A simple leading particle explanation for linear momentum transfer systematics

“…Consider the target 23su. The average nucleon cut-off energy e of the secondary would be such that 0.75e=Vo+l/2B c. For eF=38MeV BN=8 MeV and Bc=12 MeV [23] this becomes e = 69 MeV. If the secondary was ejected from the Fermi sea and had an average energy of 3/5 eF = 23 MeV, it has gained 46 MeV.…”

Inadequacy of the statistical model: Some evidence for compound nuclei in the A $ \approx$ 150 and Ex $ \approx$ 100-200 MeV region

“…Different prescriptions were also used for the level density parameter a ν : 1) a constant value ranging from A/6 to A/12, which provides a reasonable reproduction of the proton and alpha particle spectra; 2) the inclusion of shell effects [19] with a damping term [20,21] as a function of the excitation energy and 3) a temperaturedependent prescription [22]. Transmission coefficients derived from 1) optical model and 2) fusion systematics (FS) [23] were used. To modulate the particle-fission competition, different values of the fission delay and a f /a ν were adopted as well.…”

Decay of the compound nucleus179Au formed in the cold fusion reaction90Zr+89Y

“…We used the parameter value A R = 0.09 fm in order to calculate the transmission coefficients for the two systems of interest here. An uncertainty range of 0.03 fm__<AR<0.14 fm seems to be indicated on the basis of the results of [1] …”

“…particles and protons were calculated according to Vaz and Alexander [1]. These authors fitted measured cross sections for the fusion of protons and e particles with various spherical nuclei.…”

“…For the process reverse to evaporation, namely the fusion * This work is part of the Ph.D. thesis of U. Gollerthan of protons and e particles, respectively, with stable nuclei in their ground states, Vaz and Alexander [1] in a comprehensive treatment of existing experimental data have deduced nuclear interaction potentials. Taking these potentials as a reference, in many papers [2-10] a significant reduction of the barrier against the emission of charged particles has been deduced by comparing the measured energy distributions of charged particles with calculations based on the statistical model.…”